Several different types of data cables are in use today. Some data cables utilize optical fibers to transmit light signals, while others use conductors to convey electrical data signals. Depending on the location, to effectively convey data signals from one location to another, a conductive data cable must minimize or prevent moisture inside the data cable since high moisture levels can degrade conductivity and result in loss of data or data distortion. Depending on the construction of the particular data cable, the introduction of moisture can result in a short circuit, an increase in the data cable's capacitance, an increase in signal attenuation, or in the complete failure of the data cable.
Moisture can penetrate to the interior of the data cable in several different ways. Water may enter through a failure in a data cable's jacket. Water may also enter through a cable end, where a cable connector is attached. Mechanical impacts, electrical arcs, or lightning may breach the jacket that protects the data cable or the joint where one data cable joins another. Water may then flow through the breach towards the core of the data cable and longitudinally along the length of the data cable. Also, changes in ambient conditions may lead to differences in water vapor pressure between the interior and the exterior of the data cable. The difference in vapor pressure may then cause moisture to diffuse into the interior of the data cable. Eventually, there may be an undesirable level of moisture inside the cable or the insulation.
Various methods have been used to block water. One method of protecting data cables against water penetration is to provide a layer of plastic or polymeric material. In a cable insulated by a polymeric material, the polymeric material, when submerged in water can absorb water, causing problems in dielectric properties and wetting of the conductor (light or electrical).
Another method of protecting a data cable against water penetration is to use water swellable materials. However, when water swellable materials are exposed to high humidity over a long period of time, they expand by as much as three times their original volume. Associated dielectric properties of water swellable materials, such as dissipation factor and dielectric constant, change as water swellable materials absorb moisture. The water swellable materials are generally in close proximity to the insulated conductors of the data cable. Thus, changes in the dielectric properties of the water swellable materials affect the dielectric properties of conductive data cables, and changes in the dielectric properties of conductive data cables affect their data transmission capabilities. Therefore, when the dielectric properties of the water swellable material change, the change affects the data transmission capabilities of conductive data cables.
Thus, there is a need for a cable covering composition that provides low water absorption, while at the same time retaining high tensile strength and elongation retention properties upon fluid immersion protection.